COMET

A comet is an icy small Solar System body that, when passing close to the Sun, heats up and begins to outgas, displaying a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of loose collections of ice, dust, and small rocky particles. The coma and tail are much larger, and if sufficiently bright may be seen from the Earth without the aid of a telescope. Comets have been observed and recorded since ancient times by many different cultures.

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Encke's Comet loses its tail

Breaking up of 73P/Schwassmann–Wachmann in 1995. This animation covers three days.

Halley's Comet appeared at the Battle of Hastings in 1066 (Bayeux Tapestry).

From ancient sources, such as Chinese oracle bones, it is known that their appearances have been noticed by humans for millennia. Until the sixteenth century, comets were usually considered bad omens of deaths of kings or noble men, or coming catastrophes, or even interpreted as attacks by heavenly beings against terrestrial inhabitants.

Aristotle believed that comets were atmospheric phenomena, due to the fact that they could appear outside of the Zodiac and vary in brightness over the course of a few days. Pliny the Elder believed that comets were connected with political unrest and death.

comet nucleus

Rosetta

Rosetta is a robotic spacecraft built and launched by the European Space Agency to perform a detailed study of comet 67P/Churyumov–Gerasimenko. It is part of the ESA Horizon 2000 cornerstone missions and is the first mission designed to both orbit and land on a comet.

Rosetta was launched in March 2004 on an Ariane 5 rocket and will reach the comet by mid-2014. The spacecraft consists of two main elements: It comprises a large orbiter, the "Rosetta space probe" which features 12 instruments, and a robotic lander named "Philae", with a further 9 instruments.[1] The Rosetta mission will orbit 67P for 17 months and is designed to complete the most detailed study of a comet ever attempted.

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Trajectory of the Rosetta Space Probe

The probe is named after the Rosetta Stone, as it is hoped the mission will help form an idea of how the Solar System looked before planets formed. The lander is named after the Nile island Philae where an obelisk was found that helped decipher the Rosetta Stone. The spacecraft has already performed two successful asteroid flyby missions on its way to the comet. In 2007, Rosetta also performed a Mars swingby (flyby), and returned images. The craft completed its fly-by of asteroid 2867 Šteins in September 2008 and of 21 Lutetia in July 2010, and is presently in "hibernation" mode and on-target for its final destination. The spacecraft will remain in this state until 20 January 2014 when the hibernation exit sequence will be initiated.

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tempel 1

Tempel 1 (official designation: 9P/Tempel) is a periodic Jupiter-family comet discovered by Wilhelm Tempel in 1867. It completes an orbit of the Sun every 5.5 years. Tempel 1 was the target of the Deep Impact space mission, which photographed a deliberate high-speed impact upon the comet in 2005. It was re-visited by the Stardust spacecraft on February 15, 2011.

Tempel 1 was discovered on April 3, 1867, by Wilhelm Tempel, an astronomer working in Marseille. At the time of discovery, it approached perihelion once every 5.68 years (designations 9P/1867 G1 and 1867 II). It was subsequently observed in 1873 (9P/1873 G1, 1873 I, 1873a) and in 1879 (1879 III, 1879b).

Photographic attempts during 1898 and 1905 failed to recover the comet, and astronomers surmised that it had disintegrated. In fact, its orbit had changed. Tempel 1's orbit occasionally brings it sufficiently close to Jupiter to be altered, with a consequent change in the comet's orbital period. This occurred in 1881 (closest approach to Jupiter of 0.55 AU), lengthening the orbital period to 6.5 years. Perihelion also changed, increasing by 50 million kilometres, rendering the comet far less visible from Earth.

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Tempel 1 in X-ray light by Chandra

Comparison of Deep Impact and Stardust photos of a smooth elevated feature on the surface of the nucleus showing recession of icy cliffs at the margins.

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Stardust was a 300-kilogram robotic space probe launched by NASA on February 7, 1999. Its primary mission was to collect dust samples from the coma of comet Wild 2, as well as samples of cosmic dust, and return these to Earth for analysis. It was the first sample return mission of its kind. En route to Comet Wild 2, the craft also flew by and studied the asteroid 5535 Annefrank. The primary mission was successfully completed on January 15, 2006, when the sample return capsule returned to Earth.

A mission extension codenamed NExT culminated in February 2011 with Stardust intercepting comet Tempel 1, a small Solar System body previously visited by Deep Impact in 2005. Stardust ceased operations in March 2011.

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